LIMBS OF VERTEBRATES 43 



margin. The surface of the flying membrane was probably 

 covered with scales. In the bats (Fig. 99) four of the digits 



of the hand, Nos. II V, are elongated and take part in the 

 support of the flying membrane, the surface of which is either 

 naked or covered with fine hair. In the birds (Fig. 99) the 



R 2 



